(1) Field of the Invention
The invention generally relates to amperometry, i.e. the art of quantitative electroanalysis; specifically, the invention relates to an amperometric method for quantitative determination of a first electroactive and normally gaseous species (termed "EAGS"), such as elemental oxygen, and of a second electroactive and also normally gaseous species (the second "EAGS"), such as elemental hydrogen, in a normally fluid medium that may be gaseous or liquid.
(2) Description of the Prior Art
Reliable measuring or monitoring methods for determining the concentration of elemental hydrogen in the presence of oxygen are of importance wherever hydrogen is generated or used, e.g. in connection with electrolytical processes or when producing or reacting hydrogen in petrochemical or other operations because a gas mixture in which the fractions of oxygen and hydrogen exceed certain threshold limits of typically about 4% by volume may become explosive and may be dangerously unstable; this applies to mixtures of hydrogen and chlorine as well.
Determination of nitrous oxide in the presence of oxygen is another important problem within the ambit of the present invention.
Another problem of major importance is corrosiveness of water that is subjected to water-decomposing (i.e. oxygenolytic and hydrogenolytic) conditions such as, typically, exposure to radiolytic, e.g. neutronic, radiation. For example, the water used in water-moderated nuclear reactors is subject to radiolytic generation of oxygen and hydrogen but since the latter is relatively more "volatile" in such systems the oxygen concentration tends to increase and this, in turn, can be a cause for the water becoming corrosive to metallic components in contact therewith. One of the most effective methods to prevent such corrosiveness is the addition of elemental hydrogen in well-controlled quantities so that the hydrogen will act as a scavenger for the elemental oxygen.
Of course, amperometric methods for determining such EAGS individually, i.e. not in the same fluid or only after chemically or otherwise separating one from the other, are conventional, and membrane-enclosed amperometric cells (also termed "MEACs" for short) have been used for detection of either oxygen and hydrogen, notably since a simple and reliable hydrogen sensing method and apparatus have been disclosed by Applicant (cf. EP - A - 124,818).
Further, various methods of monitoring two substances or gases have been disclosed in French Patent No. 2,399,021 (corresponding with U.S. Pat. No. 4,197,853), U.S. Pat. No. 4,315,753 and in European Patent Application Nos. 122,511, 124,818 and 205,399.
However, insofar as amperometric determination of different EAGS is concerned, such methods tend to be rather complicated in that they involve chemical conversion or difficult and limiting operation requirements including specified membrane thicknesses and/or electrode operation at differing potentials. The last mentioned requirement is particularly undesirable for any routine-type measuring or monitoring application because changing the operating potential of a sensing electrode will introduce long delays because of the relative large capacitance of the sensing electrode and the time required for charging or discharging upon a change of the operating potential.